1. Field of the Invention
This invention relates to an electron beam apparatus using electron-emitting devices and it also relates to a method of driving such an apparatus.
2. Related Background Art
There have been known two types of electron-emitting device: the thermionic type and the cold cathode type. Of these, the cold cathode type refers to devices including field emission type (hereinafter referred to as the FE type) devices, metal/insulation layer/metal type (hereinafter referred to as the MIM type) electron-emitting devices and surface conduction electron-emitting devices. Examples of FE type devices include those proposed by W. P. Dyke & W. W. Dolan, "Field Emission", Advances in Electron Physics, 8, 89 (1956) and C. A. Spindt, "Physical Properties of Thin-Film Field Emission Cathodes with Molybdenum Cones", J. Appl. Phys., 47, 5248 (1976).
Examples of MIM devices are disclosed in various papers including C. A. Mead, "Operation of Tunnel-Emission Devices", J. Appl. Phys., 32, 646 (1961).
Examples of surface conduction electron-emitting devices include one proposed by M. I. Elinson, Radio Eng. Electron Phys., 10 (1965). A surface conduction electron-emitting device is realized by utilizing the phenomenon that electrons are emitted by a small thin film formed on a substrate when an electric current is forced to flow in parallel with the film surface. While Elinson proposes the use of an SnO.sub.2 thin film for a device of an this type, the use of an Au thin film is proposed in G. Dittmer, "Thin Solid Films", 9, 317 (1972), whereas the use of In.sub.2 O.sub.3 /SnO.sub.2 and of carbon thin film are discussed respectively in M. Hartwell and C. G. Fonstad, "IEEE Trans. ED Conf.", 519 (1975) and H. Araki et al., "Vacuum", Vol. 26, No. 1, p. 22 (1983).
FIG. 26 of the accompanying drawings schematically illustrates a typical surface conduction electron-emitting device proposed by M. Hartwell. In FIG. 26, reference numeral 121 denotes a substrate. Reference numeral 122 denotes an electroconductive thin film normally prepared by producing an H-shaped thin metal oxide film by means of sputtering, part of which eventually makes an electron-emitting region 123 when it is subjected to a current conduction treatment referred to as "energization forming" as will be described hereinafter. In FIG. 26, the narrow film arranged between a pair of device electrodes has a length G of 0.5 to 1 mm and a width W' of 0.1 mm.
Conventionally, an electron emitting region 123 is produced in a surface conduction electron-emitting device by subjecting the electroconductive thin film 122 of the device to a preliminary treatment, which is referred to as "energization forming". In an energization forming process, a constant DC voltage or a slowly rising DC voltage that rises typically at a rate of 1 V/min. is applied to given opposite ends of the electroconductive thin film 122 to partly destroy, deform or transform the film and produce an electron-emitting region 123 which is electrically highly resistive. Thus, the electron-emitting region 123 is part of the electroconductive thin film 122 that typically contains a fissure or fissures therein so that electrons may be emitted from the fissures. Note that, once subjected to an energization forming process, a surface conduction electron-emitting device comes to emit electrons from its electron emitting region 123 whenever an appropriate voltage is applied to the electroconductive thin film 122 to make an electric current run through the device.
Known surface conduction electron-emitting devices include, beside the above-described device of M. Hartwell, one comprising an insulating substrate, a pair of oppositely disposed device electrodes of an electroconductive material formed on the substrate and a thin film of another electroconductive material arranged to connect the device electrodes. An electron-emitting region is produced in the electroconductive thin film when the latter is subjected to energization forming. Techniques that can be used for energization forming include that of applying a slowly rising voltage as described above and that in which a pulse voltage is applied to an electron-emitting device and the wave height of the pulse voltage is gradually raised.
The intensity of the electron beam emitted from an electron-emitting device can be remarkably raised by carrying out an activation process on the electron-emitting device that has been subjected to an energization forming process. In an activation process, a pulse voltage is applied to the device that is placed in a vacuum chamber so that carbon or a carbon compound may be produced on the device by deposition at a location close to the electron-emitting region from an organic substance existing in the vacuum of the vacuum chamber.
Japanese Patent Application Laid-Open No. 6-141670 discloses a surface conduction electron-emitting device, its configuration and a method of manufacturing such a device.
However, when surface conduction electron-emitting devices are used in a flat type image-forming apparatus, the ratio of the electric current generated as a result of electron emission (emission current Ie) from the device to the electric current running through each device (device current If) is preferably made as large as possible in order to improve the electron emission efficiency of the device from the viewpoint of achieving a good quality for displayed images and, at the same time, reducing the power consumption rate of the device. A large emission current to device current ratio is particularly important for a high definition image-forming apparatus comprising a large number of pixels and is realized by arranging a large number of electron-emitting devices because such an apparatus inevitably consumes power at an enhanced rate and a considerable portion of the substrate of the apparatus that carries the electron-emitting devices thereon is occupied by wires connecting the devices. If each of the electron-emitting devices shows an excellent electron-emitting efficiency and consumes little power, smaller wires can be used, to provide a higher degree of freedom in designing the overall image-forming apparatus.
Further, in order to produce bright and clear images, not only the electron-emitting efficiency but also the emission current Ie of each device has to be improved.
Finally, each electron-emitting device is required to maintain its good performance of electron emission for a prolonged period in order for the image-forming apparatus comprising such devices to operate reliably for a long service life.